HR: 1340h
AN: V43A-1104    [Abstracts]
TI: Primary magnetic fabric in an ultrabasic body embedded in high-pressure felsic granulite from the Moldanubian Zone, European Variscides: resistance to exhumation-related medium- pressure granulite-amphibolite facies metamorphism
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: Agico, Inc., Jecna 29a, Brno, CZ-62100, Czech Republic
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: Institute of Petrology and Structural Geology, Charles University, Albertov 6, Praha, CZ- 12843, Czech Republic
AU: Faryad, S W
EM: faryad@natur.cuni.cz
AF: Institute of Petrology and Structural Geology, Charles University, Albertov 6, Praha, CZ- 12843, Czech Republic
AU: Jerabek, P
EM: jerabek1@natur.cuni.cz
AF: Institute of Petrology and Structural Geology, Charles University, Albertov 6, Praha, CZ- 12843, Czech Republic
AU: Chlupacova, M
EM: mchlupacova@chello.cz
AF: Agico, Inc., Jecna 29a, Brno, CZ-62100, Czech Republic
AB: About 11 x 5 m large body of serpentinized peridotite-clinopyroxenite, enclosed in felsic granulite, occurs in a quarry near the village of Bory (Moldanubian Zone of Western Moravia). The granulite is characterized by the presence of lighter quartz and feldspar-rich bands-layers (up to 10 cm width) alternating with gray stripes consisting of feldspars, quartz, garnet and kyanite. The presence of biotite and sillimanite, that together with quartz ribbons and relic kyanite define the foliation, depends on the degree of retrogression in amphibolite facies conditions. The ultramafic rocks show various degree of serpentinization of olivine and orthopyroxene and of amphibolization of clinopyroxene. The high-temperature textural modification of the clinopyroxenite is characterized by formation of exsolution lamellae of orthopyroxene and garnet in clinopyroxene or recrystallization of large (up 10 mm) clinopyroxene crystals into fine-grained matrix with garnet. The anisotropy of magnetic susceptibility (AMS) was used to investigate the fabrics of both the ultrabasic body and the host granulite. Through investigating low-field variation of the AMS, one could resolve the AMS into the field-independent component due to mafic silicates and pure magnetite in the ultrabasic body and due to mafic silicates in the host granulite and the field-dependent component due to Fe-Ti oxides in the ultrabasic body and due to pyrrhotite in granulite. The field-independent and field-dependent components are coaxial both within ultrabasite and within granulite. On the other hand, they show different orientations in ultrabasite and granulite. In granulite, the magnetic foliation is roughly parallel to the metamorphic schistosity and banding that show relatively stable orientation throughout the entire quarry. The magnetic lineation is rather scattered, but still relatively near the mesoscopic lineation defined by mineral alignment. The AMS ellipsoids are mostly oblate to very oblate, but some of them are also prolate. The degree of AMS is variable, ranging from low to relatively high. In the ultrabasic body, the magnetic foliation is relatively scattered in spatial orientation, but mostly oriented differently than that in granulite. The magnetic lineation is also scattered, but still relatively well defined spatially. Again, its orientation is mostly different than that of granulite. The shapes of the AMS ellipsoid are variable, ranging from very prolate to clearly oblate. The degree of AMS is relatively high, slightly higher than that in granulite. Consequently, the magnetic fabric in the ultrabasic body is different from that in the host granulite even though they experienced at least partially common structural history. The componental movements forming the granulite fabric were evidently not strong enough to strongly overprint the magnetic fabric of ultrabasite. The ultrabasite is therefore strong enough to maintain its pre-metamorphism fabric even at such high temperatures and strong pressure that are characteristic of granulite facies metamorphism.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting